DESCRIPTION: The transition from suckling to adult ingestion is a challenge facing all young mammals. In rats, this transition is made within weeks of birth and understanding the mechanisms by which rat pups normally develop from complete dependence on the dam to completely independent intake regulation may provide valuable insight for intervention in failures to accomplish the suckling to weaning transition in mammals in general. Early in a rat pup's life, the physiological signals which modulate ingestion appear to be few, but prior to weaning pups begin to modulate their intake in response to a signal related to changes in energy metabolism. The experiments in this proposal test questions about the development of intake regulation in rat pups using this emergent metabolic responsiveness. First, the role of changes in utilization of a specific metabolic fuel (fat) is tested using several pharmacological agents known to inhibit oxidation of fatty acids at several different biochemical steps. The behavioral effects of these agents are compared to their biochemical effects to test changes in the utilization of fats affect intake in young rats. Second, because physiological signals can affect ingestion at a number of behavioral levels, the ingestive behavioral components on which metabolic signals exert their effects during development is examined to test the mechanisms by which changes in the utilization of energy are translated into changes in ingestive behavior. Further, if a signal related to changes in the utilization of energy normally modulates ingestion, then feeding induced by metabolic blockers should be similar to feeding induced by energy restriction (i.e. food deprivation). Thus, similar pre- and post-absorptive physiological signals should suppress intake stimulated by food deprivation and pharmacological blockade of metabolism. This hypothesis is tested by examining the physiological signals suppressing intake stimulated by metabolic blockers. Finally, the neural mechanisms involved in translating physiological changes related to energy utilization into increases in ingestive behavior are tested.